A workpiece typically of silicon or a ceramic is cut using a sawing machine assembled with a saw wire. The saw wire travels in one direction or in two directions (in a reciprocating direction) and, when brought into contact with the workpiece, can slice the workpiece in an arbitrary width.
Known techniques for cutting a workpiece include a technique of cutting the workpiece while spraying, on a saw wire, a slurry containing abrasive grains (customary technique 1), where such abrasive grains are hereinafter also referred to as “loose abrasive grains”; and a technique of cutting the workpiece using a saw wire including a base wire bearing fixed abrasive grains (fixed-abrasive wire), where the abrasive grains are adhered and fixed to the surface of the base wire (customary technique 2). According to the former technique, the workpiece cutting is performed by introducing the loose abrasive grains contained in the sprayed slurry into between the workpiece and the saw wire, thereby accelerating the abrasion of the workpiece, and accelerating grinding of the workpiece. In turn, according to the latter technique, the workpiece cutting is performed by allowing the abrasive grains fixed to the surface to accelerate the abrasion of the saw wire and the workpiece, and thereby accelerating the grinding of the workpiece.
Patent Literature 1 discloses a technique of preparing a wire including a steel wire (e.g., a high-carbon steel) and an abrasive-grain-carrier resin coating covering the circumferential surface of the steel wire; and cutting a workpiece using the wire while embedding sprayed abrasive grains in the resin coating (customary technique 3). Patent Literature 1 describes that “The wire-saw cutting using loose abrasive grains involves coating the wire circumferential surface with an abrasive-grain-carrier resin coating, spraying loose abrasive grains, and bringing the loose abrasive grains into a region where the wire and the workpiece are in contact with each other while allowing the sprayed loose abrasive grains to intrude into the abrasive-grain-carrier resin coating. When the wire-saw cutting according to this technique is performed, the loose abrasive grains intrude into the abrasive-grain-carrier resin coating being relatively softer than the abrasive grains and, in this state, are brought into between the workpiece and the saw wire. This allows the saw wire to carry the loose abrasive grains more satisfactorily and can stably bring (introduce) the loose abrasive grains into between the workpiece and saw wire. The saw wire according to the present invention, therefore, enables production of high quality products (sliced articles) in high yields.” In addition, Patent Literature 1 also describes that “fine particles may be incorporated in the abrasive-grain-carrier resin coating, which fine particles are made from a hard inorganic substance such as zirconia or alumina”; and refers to that “this suppresses the abrasion of the abrasive-grain-carrier resin coating itself and provides an expectation of the abrasive-grain-carrier resin coating to have further better carrying capability of the loose abrasive grains, because the abrasive-grain-carrier resin coating has regions having different hardness, i.e., a region of the resin coating alone and a region with the inorganic fine particles.”
Cut articles prepared by cutting silicon with a saw wire are used typically as solar cell substrates. The resulting cut articles, however, may bear a damaged layer (also called “affected layer”) formed on a cut surface upon cutting. Patent Literature 2 points out that the damaged layer, if remaining, may adversely affect junction quality with respect to the substrate and inhibit the solar cell from exhibiting sufficient properties as a solar cell. To prevent this, the damaged layer should be removed.